Gasoline production process

ABSTRACT

HIGH OCTANE GASOLINE IS PRODUCED BY ISOMERIZING A C4 THROUGH C6 PARAFFIN FRACTION FROM A STRIAGHT RUN GASOLINE, THE HIGHER BOILING PORTION OF THE STRAIGHT RUN GASOLINE IS PASSED INTO A REFORMING ZONE. THE EFFLUENT FROM THE ISOMERIZATION ZONE IS PASSED INTO A MOLECULAR SIEVE SEPARATION ZONE WHICH SEPARATES NORMAL PARAFFINS FROM NON-NORMALS SUCH AS AROMATICS AND ISO-PARAFFINS. A PORTION OF THE EXTRACTED NORMAL PARAFFINS ARE THEN RECYCLED TO THE ISOMERIZATION ZONE TO EFFECT FURTHER PRODUCTION OF BRANCHED CHAIN PARAFFINS. THE RAFFINATE MATERIAL RECOVERED FROM THE MOLECULAR SIEVE SEPARATION ZONE IS SUFFICIENTLY HIGH IN OCTANE NUMBER TO BE UTILIZED AS A CLEAR GASOLINE. THE REFORMING AND ISOMERIZATION ZONE EFFECT THE CONVERSION OF THE RESPECTIVE FEED TO THOSE ZONES THROUGH THE USE OF SUITABLE CATALYTIC COMPONENTS. THE SEPARATION ZONE   UTILIZES A TYPE A CRYSTALLINE ALUMINOSILICATE TO SELECTIVELY EXTRACT NORMAL PARAFFINS FROM A FEED CONTAINING NORMAL PARAFFINS AND OTHER NON-NORMAL COMPONENTS.

Jan. 15, 1974 w. H. DAVIS 3,785,955

GASOLINE PRODUCTION PROCESS Filed Dec. 1, 1971 United States Patent O U.S. Cl. 208-80 7 Claims ABSTRACT OF THE DISCLOSURE High octane gasoline is produced by isomerizing a C through C parafiin fraction from a straight run gasoline, the higher boiling portion of the straight run gasoline is passed into a reforming zone. The efliuent from the isomerization zone is passed into a molecular sieve separation zone which separates normal paraffins from non-normals such as aromatics and iso-parafiins. A portion of the extracted normal paraflins are then recycled to the isomerization zone to eifect further production of branched chain paraflins. The raflinate material recovered from the molecular sieve separation zone is suificiently high in octane number to be utilized as a clear gasoline.

The reforming and isomerization zone elfect the conversion of the respective feed to those zone through the use of suitable catalytic components. The separation zone utilizes a Type A crystalline aluminosilicate to selectively extract normal paraffins from a feed containing normal parafiins and other non-normal components.

BACKGROUND OF THE INVENTION Field of the invention The field of art to which this invention pertains is hydrocarbon processing. Specifically, the field of art to which this invention pertains is refinery processing in which a combination processing sequence made up of catalytic isomerization and reforming of the light and heavy portions respectively of a traight run gasoline followed by extraction of the normal paraffins from the resulting reformate and isomate to produce the relatively high octane gasoline.

Description of the prior art In prior art processes in which a straight run gasoline is used as a feed stock, a paraffin isomerization zone and a naphtha reforming zone can be used to catalytically alter the hydrocarbon makeup of the two respective streams. In many instances the effluents from both the reforming and the isomerization zone excluding the C C hydrocarbons can be combined and passed into a normal parafiin separation zone where non-normal gasoline components such as high octane isoparafiins and aromatic compounds are recovered as gasoline components. The low octane grade normal components from the normal paraflin separation zone are then recycled to the isomerization zone for upgrading to higher octane components and eventually recovered from the separation zone. This type of flow scheme does not allow low grade isoparaffins such as the methyl pentanes which leave the reforming zone to be upgraded in the isomerization zone since they are removed from the process after passing through the normal paraflin separation zone being recovered a nonnormal gasoline components.

I propose as my invention placing a stripping tower after the reforming zone to separate low octane isoice parafiins from the reformate eflluent and pass them into the isomerization zone to be upgraded. Any normal paraffins present in this stream will also be upgraded. The particular low grade isoparaffins which are removed from the reforming zone include Z-methylpentane and S-methylpentane which have research clear octane members (RON) of about 73.4 and 74.5 respectively. By converting these to higher octane components in the isomerization before they are recovered as non-normal gasoline from the normal paraflin separation zone. the gasoline produced can be substantially higher in octane rating. Additionally, the low grade normal parafiins such as normal pentane (RON-61.7) which by definition has a zero octane rating, can be converted to higher octane nonnormal paraifins. This helps reduce the normal paraffin load on the normal paraffin separation zone and also reduces the amount of normal paraffins which must be recycled from the paraffin separation zone to the isomerization zone.

In reforming-isomerization combination processes which utilize straight run gasoline feed stocks which contain over about 60 vol. percent paratfins, the C C and C parafiin content of the reformate is substantially high enough to justify the utilization of the stripping tower, in fact, it is preferable to use this type of arrangement in processes having straight run gasoline feed stocks which contain more than about 60 and preferably more than about 65 vol. percent paraifins.

SUMMARY OF THE INVENTION It is an object of the present invention a combination process in which a separation zone is placed after a reforming zone to separate low grade parafiins therefrom, pass them into an isomerization zone in order to upgrade both normal and isoparaflins to high octane isoparaflins.

The present invention is generally described as a combination process for the production of high octane gasoline. More specifically the combination includes an isomerization zone and a reforming zone operated in a parallel flow configuration to convert light paratfins and heavy naphtha to high octane isomerate and reformate. The reformate i then separated into a light paraffinic portion and a heavier reformate portion. The light reformate portion is passed into the isomerization zone after which the effluent from the isomerization zone and the remaining reformate material are combined and passed into a normal parafiin separation zone which acts upon its feed stock to selectively remove normal paraifins from material fed to it. A portion of the normal paratfins are recycled to the isomerization zone to be upgraded. The basic purpose of this flow scheme is to produce a gasoline containg a minimum of normal parafiinic components.

BRIEF DESCRIPTION OF DRAWING The attached drawing shows the arrangement of the present combination process. The basic zones of operation as claimed are isomerization zone 2, reforming zone 3, stripping zone 5, and paraffin separation zone 7. Fractionators 1 and 8 are utilized to separate hydrocarbon feed stock into lighter and heavier components. Separators 4 and 6 are utilized to separate gaseous materials such as hydrogen and light hydrocarbon gases from liquid hydrocarbons.

The feed stock which is utilized in this process flows through line 9 into fractionation zone 1. Fractionation zone 1 allows the feed stock to be separated into a light naphtha portion which passes thorugh line 10 into isomerization zone 2 and a heavy naphtha portion of the feed which passes out of the fractionation zone via line 22 and into reforming zone 3.

The heavy naphtha portion of the feed stock passes through line 22 in admixture with hydrogen containing gas from line 23. The reforming zone is operated at conditions to effect the production of aromatic hydrocarbons from parafiins and cycloparafiins. The efiluent from the reforming zone 3 passes via line 25 into separator 4 which separates gaseous hydrocarbons from liquid hydrocarbons. Any excess hydrogen or light gases produced in the process can be withdrawn via line 24. The remaining hydrogen rich gas passes via line 23 to be combined with the feed. The normally liquid portion of the reformate passes out of separator 4 via line 26 into stripping zone 5 and is generally made up of hydrocarbons having from 4 up to about 15 or more carbon atoms per molecule. Stripping zone 5 effects the separation of liquid reformate into a light paraflin portion which passes via line 12 into line and eventually into isomerization zone 2. The remaining reformate material passes via line 16 into line 17 and into paraffin separation zone 7.

Parafiin separation zone 7 allows the combination of isomerate and reformate passing through line 17 to be separated into a non-normal gasoline component which passes out of the separation zone via line 18 for recovery. The normal paraffins which are preferably selectively adsorbed by the adsorbent in the separation zone pass out of that zone via line 19 and into fractionation zone 8 where they are separated into normal paraffins having molecular weights of seven or higher carbon atoms per molecule which pass out of the fractionation zone through line 20 and recovered. The lighter normal paraflins, generally C and C paraffins, pass via line 21 into line 12 and eventually into isomerization zone 2. Some of the light paraffins can be recovered via line 27.

The efiluent from the isomerization zone 2 flows through line 13 and into separator 6 which separates liquid hydrocarbons from normally gaseous hydrocarbons. The heavier liquid hydrocarbons of the isomerate pass through line to be combined with the material passing from the reforming zone via line 16 and eventually are passed into the separation zone via line 17. The heavy materials which pass through line 15 generally consist of isomerized C and C hydrocarbons. The lighter hydrocarbons and normally gaseous hydrocarbons which generally comprise hydrogen through propane are removed from the separator via line 11 and recycled to the isomerization zone. A portion of the gaseous materials may be vented via line 14 when excess amounts are made.

The above brief description of the inventive process combination of this invention is shown in a simplified form. Deleted from the attached drawing are such necessary components to effect the process as compressors, pumps, valves, pressure regulating means, and heating means. Pre-heaters can be present before the isomerization and reforming zone along with compressors on the recycle stream which pass from their respective separation zones through the isomerization and reforming zones. Flow control valves can be present on any or all of the streams passing into, out of and between various reaction zones as described on the drawing. The paraffin separation zone 7 can be a swing-bed system or preferably the fixed-bed simulated moving-bed countercurrent flow systems known in the art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to more adequately describe the invention, the following definitions are utilized throughout this specification and in the attached claims. The term straight-run gasolines refers to naphtha feed stocks having boiling ranges varying from about F. up to amout 440 F. or higher. Specifically, straight-run gasolines are derived from crude sources directly without intervening processing steps except for scrubbing and/or hydrogenation to remove sulfur, nitrogen or olefinic contaminants. The term naphtha shall include straight run gasolines, cracked streams containing low quantities of aromatics, saturated reformates having the aromatic portion thereof separated by extraction, etc. Typically, straight run gasolines contain from 0 to 10 vol. percent aromatics, about 15 to about 30 vol. percent cycloparafiins and from about 15 to about 75 vol. percent paraffins. Depending upon the source of the crude oil or from which type of a processing unit the naphtha has been derived, the volume ratios of paraffins to naphthenes to aromatics can vary widely as can be noticed in inspections of the relatively highly parafiinic Middle East crudes to the low in paraffinic crudes such as the Pennsylvania crudes. The term heavy naphtha is the heavy portion of the straight run or naphtha feed stock and is made of the C and heavier feed components. The term light naphtha is the portion of the naphtha feed containing C to C hydrocarbons (generally isoand normal paraflins) The light paraffin portion of the reformate stream shall include the C through C hydrocarbons including C isoand normal paraffins. In most instances this material contains large quantities of normal paraffins. In some instances this material may contain large quantities of non-normal parafiins such as methyl pentane. The term isomerate shall refer to liquid hydrocarbon eflluent removed from the catalytic isomerization zone. Typically isomerates include C through C hydrocarbons having a relatively large quantity of isoparaffinic substances. In some instances small portions of normal parafiins may be present. The term reformate refers to liquid hydrocarbon effluent removed from the reforming zone. Typically, reformates have boiling ranges anywhere from F. to about 440 F., contain large concentrations of aromatic hydrocarbons, smaller quantities of paraffins and even smaller quantities of cycloparafiins. The reforming zone effects the dehydrogenation of cycloparaffins and the dehydrocyclization of parafiins to form aromatics.

The catalysts which can be used in the reforming zone include refractory inorganic oxide carriers containing one or more reactive metals components thereon. Inorganic refractory oxides which can be used as carriers include alumina, crystalline aluminosilicates, such as the faujasites, the type X or type Y zeolites or mordenite, or combinations of alumina and the crystalline aluminosilicates or silica and the crystalline aluminosilicates. Metallic components of reforming catalysts generally recognized in the art as being favorable include the Group VIII and Group IV metals. Rhenium, tin and lead have also been shown to have catalytic properties when used with platinum. Combined halogens may also be used as one of the catalytic components. The halogens which can be used include chlorine, fluorine, bromine, iodine, or mixtures thereof.

Effective reforming operating condtions include temperatures in the range of from about 800 F. up to about 1100 F. and preferably between about 850 and 1050 F., liquid hourly space velocities in the range of from about /2 to about 15 and preferably in the range of about 1 to about 5. The quantity of hydrogen recycle gas which is charged with the hydrocarbon feed stock in the reforming zone is generally present in amounts of about /2 to about 20 moles of hydrogen per mole of hydrocarbon feed and preferably from about 4 to about 12 moles of hydrocarbon per mole of hydrocarbon feed. The reforming zone may utilize flow systems familiar to those skilled in the art such as fluidized type processes, moving bed type processes, fixed bed processes, etc. Particularly suitable processes include fixed bed systems in which the catalyst is disposed in one or more reaction zones. Other suitable reforming operations include the newly introduced moving bed systems in which a small portion of catalyst is continuously being removed, regenerated and returned to the reforming zone.

The reforming zone eflluent or reformate is generally passed into a liquid-gas separator where it can be separated to remove lighter weight components from the heavier weight liquid components of the reformate. The recycle gas which is used in the reforming zone can easily be separated from light components. A certain amount of the recycle gas is generally moved from the reforming system to maintain a given constant operating pressure. Reforming zones pressures are generally in the range of from about to about 1500 pounds per square inch. New operating techniques have tended to show that low pressures may be utilized so that pressures lower than 10 p.s.i. are contemplated in the future.

Isomerization conditions may be effected in the isomerization zone to convert some of the lower grade isoparafiins and normal parafiins to higher grade branched isoparaffins. Temperatures used will generally be dictated by the particular isomerization catalyst disposed within the isomerization zone and will be within the range of from about 200 F. to about 800 F. The pressure selected for isomerization will be within the range of from about 100 to about 2,000 lbs. per square inch. The liquid hourly space velocity which is defined as the volume of liquid charge per hour per volume of catalyst disposed Within the reaction zone will range anywhere from about one to about or more. Hydrogen is utilized to minimize cracking and to maintain the surface of the catalyst in a carbon-free condition. Therefore, the quantity of hydrogen utilized remains anywhere from about A to about 10 or more moles of hydrogen per mole of hydrocarbon fed to the process. Consumption of hydrogen is generally small and will be within the range of about 30 to about 100 s.c.f. of hydrogen per barrel of total liquid hydrocarbon charge to the isomerization zone reaction zone.

The catalyst located within the isomerization zone may be any suitable carrier material with an acid-acting component and a hydrogenation component. The carrier material may be selected from various refractory inorganic oxides including silica, alumina, silica-alumina, silicaalumina magnesia, silica-alumina zirconia, alumina zirconi, silica zirconia, crystalline aluminosilicates including the type X and type Y, mordenites and mixtures of the crystalline aluminosilicates with either alumina or silica or both, etc. These various carrier materials will have surface areas ranging from about 25 to 500 square meters per gram depending upon their method of preparation. Of the various possible carrier materials, alumina is particularly preferred and especially gamma-alumina having a surface area of from about 150 to 450 square meters per gram. When gamma-alumina is utilized as a carrier material, acidacting components may be added thereto by incorporating therewith quantities of a combined halogen. The amount of combined halogen can be varied anywhere from about 0.01 to about 8% or more by weight calculated as the element based upon the weight of the carrier material. Both fluorine nd chlorine may be used to supply combined halogen. The hydrogenation component is generally combined with the carrier material after the carrier material has been formed. The hydrogenation component used will generally be selected from the group consisting of Group VIB and Group VIII metals or mixtures thereof. Such hydrogenation components include chromium, molybdenum, tungsten, iron, cobalt, nickel, and the platinum group metals including platinum, palladium, ruthenium, rhodium, osmium, and iridium. The platinum group metals are preferred and of these metals platinum is particularly preferred. The hydrogenation component of the catalytic composite is utilized in an amount anywhere from about 0.01 to about 10% by weight calculated as the elemental based upon the weight of the carrier material.

The parafiin separation zone utilized in the process of this invention includes an apparatus designed to selectively adsorb normal parafiins from the material fed into this zone, in particular the parafiin separation zone effects separation of normal paraflins from non-normal hydrocarbons such as isoparaffins, cycloparafiins and aromatics by utilizing a crystalline aluminosilicate adsorbent commonly referred to as a molecular sieve.

Molecular sieves having a pore entrance diameter of about 5 angstroms units are utilized to separate normal aliphatic hydrocarbons from isoparafiins, naphthenes, aromatics and the like. The molecular sieves are composed of aluminosilicates arranged so that the pore cavities are interconnected by pore entrances of a given uniform size. The pore entrance size may be varied by utilizing a different metal within the sieves such as sodium, potassium or calcium, or in some instances by the variation in the silica to alumina ratio of the zeolite structure. Typically the structure is interconnected tetrahedra made up of silica and alumina in which the aluminum and silicon atoms share oxygen atoms. Although molecular sieves have been produced having pore entrance diameters of from about 3 to about 15 Angstrom units, is is generally desired to utilize a sieve having a uniform pore entrance size such that the normal chain hydrocarbons pass through the pore entrances while the larger non-normal hydrocarbons are excluded. Thus, the separation effected in this zone is truly on the basis of molecular sizes.

Specifically, the preferred adsorbent which is utilized in the separation zone is referred to as type A zeolite. This zeolite is particularly described in US. Pat. 2,882,243.

Zeolite A may be used in its pure stage or combined with the binder material. The particle size of the adsorbent may vary. Specifically preferred are those particles having sizes within the range of 20 to 40 mesh size.

Separating conditions are defined as the conditions at which normal parafiins may be selectively removed from the feed stream passing into the paraffin separation zone and include temperatures anywhere within the range of about ambient up to about 500 F., pressures from about atmospheric up to 500 or 1000 p.s.i.g., liquid hourly space velocities of liquid feed stocks passed into a bed of molecular sieves can vary anywhere from less than 0.01 up to values of 20 or higher. It is preferable to perform the adsorption and desorption of normal paraflins in a liquid phase, however, vapor phase operations may take place. The adsorbent may be dispersed in one or more chambers in which alternate streams of feed and desorbent material are passed to effectively allow continued extraction of normal parafiins. The separation zone may utilize a fixed bed of adsorbent having a valve arrangement to allow a continuous shifting of feed stock and desorbent input streams through the bed to simulate a moving bed system. Typically this latter type of arrangement proves to be the most efiicient use of adsorbent and allows high recoveries of normal paraifins from the feed stock along with high product purities. The fixed bed countercurrent flow schemes which can simulate a moving bed can be found described in US. Pat. 2,985,589 issued to D. B. Broughton. This patent generally describes a continuous flow process which is the preferred mode of operation of the separation zone of this process.

In some processing flow schemes vacuum desorption or gas stripping is utilized to remove selectively adsorbed normal paraflins from the adsorbent. In these instances the desorbent materials which may be utilized to strip normal parafiins from the molecular sieve adsorbent may comprise air, steam or other inert gaseous materials such as nitrogen or hydrogen or light hydrocarbon such as methane, ethane, or propane or butane. In other instances liquid desorbents may be utilized. It is preferable when using liquid desorbent, that the desorbent material be relatively easily separated from materials it desorbs and the feed stock in order to easily recover the desorbent from the raffinate and extract product streams. Specifically, light desorbents such as normal butane or mixtures of normal butane with isobutane can be utilized. Other preferred desorbents include normal pentane in admixture with iso-octane. Desorption conditions can generally include the pressure and temperature limitations described for adsorption conditions. In this specification a rafiinate material shall be referred as the feed stock material which is not selectively adsorbed by adsorbent. Typically the raffinate materials comprise nonnormal hydrocarbons such as isoparaffins, cycloparafiins, aromatics and iso-olefins. These materials should be easily separated from the desorbent material which is reused in the separation zone. The extract material is the feedstock material which is selectively adsorbed by the adsorbent and comprises normal hydrocarbons such as normal paraffins. In some instances, straight run gasoline or naphtha feed stock which is utilized in the process of this invention is first passed through a hydrogenation zone in order to render it essentially free of combined sulfur and nitrogen and olefin material. Preferably the hydrogenation takes place in a separate reaction zone at hydrogenation conditions including the use of a catalyst containing a hydrogen transfer active metal such as a platinum group component which feed and a hydrogen gas stream contact at conditions to effect the saturation of most of the olefins present in the feed and the conversion of nitrogen compounds into ammonia with sulfur being converted to hydrogen sulfide. Preferably the effluent from the hydrogenation zone is passed into the separation zone where gaseous materials are separated from liquid hydrocarbons.

The following examples are presented to better illustrate the process of this invention and are not to be used to unduly restrict the scope thereof.

EXAMPLE I Experiments were conducted utilizing a molecular sieve adsorbent in a paraflin separation zone to separate a reformate into low grade extract (normal paraffin) and a high grade gasoline rafiinate (aromatics and non-normal parafiins). The reformate used as a starting material had properties as shown in Table I below:

The reformate was then fractionated to separate a light parafiin fraction from the remaining heavier material. The light parafiin portion was representative of the portion of the reformate which is passed into the isomerization zone from the reforming zone as claimed and amounted to about 13 vol. percent of the original reformate. The composition of the light parafiin fraction is shown in Table II:

The remaining 87 vol. percent of the reformate was analyzed as shown in Table HI below:

TABLE III.- F. Reformate Boiling range IBP/EP, F. 180/402 RON 94.3

Hydrocarbon type: Vol. percen Benzene 0.4 Toluene 15.4

C aromatics 22.3 C aromatics 25.5 C naphthenes 1.4

O; isoparaflins- 8.2

O; n-paraffins 3.2

C isoparafiins 9.8

C n-paraffins 2.6

C isoparafiins 5.9

C n-parafiins 1.0 0 parafiins 1.0 Olefins 1.0

As can be seen, the light parafiins of Table II contained a total of about 18.4 wt. percent of methylpentane material which averaged around 74 RON. By passing this stream into an isomerization zone the methylpentanes can be upgraded before they are separated from the normal hydrocarbons in the normal paraffin separation zone.

The 180 F. reformate described in Table III above was subjected to a denormalizing operation using a type A molecular sieve and operating conditions generally described for the normal paraflin separation zone described above.

The denormalized fraction of the reformate described in Table III is shown in Table IV:

As can be seen above, the denormalized heavy reformate fraction was increased in octane number from 94.3 RON to 98.2 RON by the elimination of low octane normal paraflins. Also the absence of low octane 2 and 3-methylpentanes in this fraction contributed to an overall octane boost.

In other experiments in which similar heavy reformate fractions were subjected to normal paraffin separation using moleculer sieve adsorbents increase in octane numbers were as follows: from 80 RON to 89.5 RON; from 85 RON to 93 RON; from 90 RON to 96 RON; and, from 95 RON to 98.5 RON.

I claim as my invention:

1. A process for the production of gasoline from a naphtha feed stream, which process comprises the steps of:

(i) passing a light naphtha portion of said feed into an isomerization zone at isomerization conditions to effect the production of isomerate containing branched chain paraflins from normal paraflins in said light paralfinic feed;

(ii) passing a light paraflin portion of said reformate a reforming zone at reforming conditions to effect the production of a reformate containing aromatic and parafiinic hydrocarbons;

(iii) passing a light paraffin portion of said reformate to said isomerization zone at isomerization conditions to effect the production of isomerate containing branched chain paraflins;

(iv) commingling a C -C fraction of said isomerate with a heavier fraction of said reformate and passing the mixture to a normal paraffin separation zone at separation conditions to effect the selective adsorption of normal parafiins from said reformate and isomerate fractions by a crystalline aluminosilicate adsorbent having pore openings of less than about 5 angstroms diameter;

(v) recovering aromatic and branched chain paraflins from said separation zone;

(vi) recovering normal parafiins from said separation zone; and

(vii) recycling at least a portion of said recovered normal parafiins to said isomerization zone,

2. Claim 1 further characterized in that said feed stream comprises a straight run gasoline having saturated hydrocarbons having from about 4 to about 12 carbon atoms per molecule and greater than about 50% by volume paraflins.

3. Claim 1 further characterized in that said light naphtha portion of said stream contains parafiins having from about 4 to about 6 carbon atoms per molecule.

4. Claim 1 further characterized. in that said heavy portion of said feed contains hydrocarbons having from about 6 to about 12 carbon atoms per molecule.

5. Claim 1 further characterized in that said crystalline aluminosilicate adsorbent is a type A zeolite.

6. Claim 1 further characterized in that said light paraflin portion of said reformate contains hydrocarbons having from about 4 to about 6 carbon atoms per molecule.

7. A process for the production of gasoline from a straight run naphtha feed stream having hydrocarbons having from about 5 to about 15 carbon atoms per molecule, which process comprises the steps of:

(i) passing a light naphtha portion of said feed having paraffins having from about 4 to about 6 carbon atoms per molecule into an isomerization zone at isomerization conditions to effect the production of isomerate containing branched chain paraffins;

(ii) passing a heavy naphtha portion of said feed having hydrocarbons having 6 or more carbon atoms per molecule into a reforming zone at reforming conditions to effect the production of a reformate containing aromatic and parafiinic hydrocarbons;

(iii) passing a light paraflin portion of said reformate having parafiins having from about 4 to about 6 carbon atoms per molecule into said isomerization zone at isomerization conditions to effect the production of isomerate containing branched chain paraffius;

(iv) commingling a C C fraction of said isomerate with a heavier fraction of said reformate and passing the mixture to a normal paraffin separation zone at separation conditions to effect the selective adsorption of normal paraflins from said reformate and isomerate fractions by a type A crystalline aluminosilicate adsorbent;

(v) recovering aromatic and branched chain parafiins, and normal parafiins from said separation zone; and

(vi) recycling at least a portion of said recovered normal paraifins to said isomerization zone.

References Cited UNITED STATES PATENTS 3,658,690 4/1972 Graven 208-62 3,001,927 9/1961 Gerhold et al. 208-64 3,018,244 1/ 1962 Stanford et al 208-79 2,859,173 11/1958 Hess et al 208-92 2,938,936 5/1960 Belden 260-68368 2,944,001 7/1960 Kimberlin et al. 208-80 DELBERT E. GANTZ, Primary Examiner G. E. SCHMITKONS, Assistant Examiner US. Cl. X.R. 

